1. Field of the Invention
The present invention is directed to lighting modules. More specifically, the present invention is directed to lighting modules comprising light-emitting diode chips.
2. Background
A light-emitting diode (LED) is a semiconductor device that emits light when excited by electrical energy. In general, an LED comprises an LED chip disposed within a package. The LED chip is a semiconducting material (or combination of materials) impregnated, or doped, with impurities to create a p-n junction. When electrical current is passed through the LED chip in a forward-bias, electrons “jump” across the p-n junction and emit light. The package is usually a plastic or ceramic material having electrical connections to couple the LED chip to a current source. The main disadvantage of an LED package is that the thermal resistance of the package can be quite large (i.e., greater than 100° C./W), which degrades the life and performance of the LED chip. The terms “light-emitting diode chip,” “LED chip,” “chip,” or “LED die” are used to refer to the semiconducting p-n junction, and thereby differentiate from the term LED, which generally includes both a chip and its packaging.
LEDs are more efficient light sources than incandescent light sources. However, one challenge with using LEDs as light sources for general lighting applications is in obtaining sufficient light out of an individual LED chip. In other words, an individual LED chip does not provide enough light as compared to other light sources such as, for example, tungsten filaments. However, when several LEDs are combined into an array of LEDs, the combination and cumulative effect of all the LED chips in the array produce a light source with sufficient light.
LEDs are seeing increased use in lighting applications. Early uses of LEDs in lighting fixtures have tended to employ high-power LEDs (typically, 1W chips) grouped together in what is generally referred to as a lighting module. One or more lighting modules may then be employed in a lighting fixture. In order to create a uniform light source, the LEDs must be placed close enough to “blend” light through a diffuser. Additionally, there is an increased demand to minimize the thickness of light fixtures, requiring the LEDs to be placed even closer together. As the LEDs are moved closer together, there is an increased need for exotic thermal management solutions (e.g., fans, cooling fins, heat pipes, etc.).
In addition to heating issues, lighting modules using LEDs must be designed to address optical issues such as color uniformity and binning. For example, depending on the semiconducting material used, LED chips can deliver light of different colors. In order to produce white light, two techniques are generally employed. In one technique, three LED chips (one red, one blue, and one green) are bundled together such that the cumulative output results in a white light source. The second technique employs a UV/blue LED chip coated or packaged with a phosphor. The LED chip emits light of a specific wavelength (in the UV or blue region). The emitted light excites the phosphor, which results in the emission of white light. However, when LED chips are manufactured, a single semiconducting wafer can produce LED chips of varying wavelengths. LED chip manufacturers must then employ an expensive binning procedure to organize (or bin) the LED chips by wavelength. In order to ensure uniformity, a manufacturer of LED lighting modules would require LED chips from a small range of bins. Such a limitation adds to the production costs of the lighting module.